Wikipedia:Reference desk/Archives/Science/2006 November 22

= November 22 =

distilled water
I could of course probably distill my own water for making an electrolyte but decided to check the local stores. Curiously the only distilled water was also fluoridated. (If that is the right term.) Since some references suggest adding chloride ions to a electrolytic bath of sulphuric acid and copper sulphate for copper plating either by adding sodium chloride or hydrochloric acid in relatively minute quantities I was wondering if the presence of fluoride ions might actually benefit the plating process or cause some terrible smut. 71.100.6.152 02:31, 22 November 2006 (UTC)


 * Can you not get it from your freezer?--Light current 02:38, 22 November 2006 (UTC)


 * How very strange that you cannot get distilled water! Where are you? It's very commonly available in the US (for example); people use it for steam irons and such. --jpgordon&#8711;&#8710;&#8711;&#8710; 03:14, 22 November 2006 (UTC)


 * Are you trying to get distilled water or are you trying to electroplate something? --Russoc4 03:15, 22 November 2006 (UTC)


 * Looks like he wants to make dilute H2SO4 for use in making an electrolyte for copper plating as he says. Of course an old car battery will have some of that in it!--Light current 03:32, 22 November 2006 (UTC)


 * Since my goal is making a plating bath and since I have already purchased the fluoridated water my question is really about the effect of the fluoride on the electroplating process. If it is bad then I will need to use one of the techniques of distillation. Stores in the area use to carry "pure" distilled water for irons and batteries, etc. but with sealed batteries now-a-days and the craze for bottled water only the fluoridated variety of distilled water is available where I live. All the rest is purified by reverse osmosis. 71.100.6.152 03:45, 22 November 2006 (UTC)

In regard to ice distillation techniques it would seem that one could not freeze all of the water into one large chunk without capturing some of the ions or salts between ice crystals and one would already need to have some distilled water to rinse the ice if it were slush. The process of capturing the ice crystals free of ions and salts eludes me. Please elaborate. 71.100.6.152 03:45, 22 November 2006 (UTC)


 * The water in your freezer comes from the atmospheric moisture which should be relatively free of impurites.It wont even have any flouride in it! You defrost the freezer and collect the water. 8-) Or am I missing something?--Light current 03:55, 22 November 2006 (UTC)


 * I don't know what you are missing but I don't believe it, freezer ice can definitely have a funny taste to it, I have no idea what causes it but it doesn't taste as clean as store bought ice. I think the food in your freezer can have an effect on it somehow. Vespine 04:17, 22 November 2006 (UTC)


 * The water vapor in air is a natural magnet for absorbing particles from the air, which then become part of the ice. This cleansing effect is why air seems fresher after it rains. StuRat 04:53, 22 November 2006 (UTC)


 * So that awesome "smell of rain" is actually just clean air? ☢  Ҡ i∊ ff   ⌇  ↯  04:58, 22 November 2006 (UTC)


 * its the smell of trees apparently. the plants stoma sense the humidity change and open up, letting volatile compounds float out and into our nose. Xcomradex 05:55, 22 November 2006 (UTC)


 * Actually, it's usually the soil/rocks which release the bulk of those volatile chemicals. See Petrichor. GeeJo (t)⁄(c) &bull; 08:05, 22 November 2006 (UTC)


 * And, I suppose, there's the ionization of the air, especially if the rain is accompanied by a thunderstorm. StuRat 08:12, 22 November 2006 (UTC)

Okay, well distallation aside what about the effect on plating of the fluoride? Its apparently added for the benefit of babies teeth so there can't be much but does anyone know the effect on plating? 71.100.6.152 06:25, 22 November 2006 (UTC)

WARNING! Adding sulphuric acid to fluoride will produce HydroFluroic acid - which is volatile and reputadly causes very damaging and painful burns.

That aside you need to investigate fluoride compounds of platinum - if the fluorides are insoluble that may cause problems.87.102.36.82 13:39, 22 November 2006 (UTC)Not sure where I got the impression you were using Pt - it depend on what your plating probably - don't have much expertise anyway
 * I always thought the problem with hf was that by the time you got the pain it was already attacking your bones. Plugwash 14:37, 22 November 2006 (UTC)
 * Because HF is so similar to H20 it rapidly penetrates the skin causing internal damage rather than just the surface burns caused by other acids.87.102.36.82 14:42, 22 November 2006 (UTC)

Remember that HF also attacks glass - if it's used in a glass or metal container any beneficial effect to the plating will be lost as the HF will be converted to a salt. Other than that it's useful for cleaning the metal surface in most cases. Whether or not it will improve the quality of the plating I don't know.87.102.36.82 14:46, 22 November 2006 (UTC)


 * Yeah HF is banned in most places now. Used to be used to etch those nice etched windows yuo used to see in pubs--Light current 22:53, 22 November 2006 (UTC)

Thanks for the warning about HF. I was aware the HF would penetrate the skin and attack bone but not that sulphuric acid would react with the fluoride in water to make HF. I'm curious now as to whether there are any other reactions which might turn fluoride in drinking water to HF since I think many municipalities stil fluorinate their drinking water supply and the bottled water I purchased is specifically intended for use by human babies. Please comment. 71.100.6.152 22:56, 22 November 2006 (UTC)
 * The fluoride in drinking water and tooth paste is in part per million or in the case of toothpaste about 0.1% - so not enough to cause any real damage - any strong acid will liberate HF from a fluoride salt (HF is a weak acid - weaker than vinegar I think). ps try smothering your hands with toothpaste then wash it off - notice a cold burning sensation?...83.100.250.186 15:44, 23 November 2006 (UTC)


 * OK then. What is the amount of dissolved undesirable elements, ions, compounds, gases etc in freezer ice. I really would like to know! 8-)--Light current 23:21, 23 November 2006 (UTC)
 * I'll ask for you - don't think anyone will notice here...

Solenoid valves in Gasoline engines?
Hi was reading up on some of the new tech patented by the auto companies recently,and was just wondering, solenoid valves are used quite commonly in diesel engines as part of the Common rail injection system. but these are relatively unheard of in petrol engines.where wheel bearings are still used to open and shut the camshafts.as is obvious,solenoid valves provide excellent variation as far as timing the fuel injection goes.so why aren't they used? Thanks. —Preceding unsigned comment added by Vikram1005 (talk • contribs)


 * Just a guess: Diesel combustion is regulated by Fuel/Air mixture ratio correlated to pressure. the only timing element available is injection.  In petrol engines, combustion timing is controlled almost exclusively by the spark.   --Tbeatty 07:21, 22 November 2006 (UTC)

how do computer processors work ?
where can i learn about internal structure of a simple processor ?


 * Did you read about computer processors per my previous answer to your question (which you deleted)? Anchoress 11:11, 22 November 2006 (UTC)


 * You know enough about Wikipedia to know how to vandalise it, but you don't know how to look things up? DirkvdM 08:10, 23 November 2006 (UTC)

Also, try howstuffworks.com:. StuRat 19:08, 22 November 2006 (UTC)


 * Here's an answer to a similar question, from the WP archive: How do processors work?


 * And here's a brief overview of PROM-based state-machine processors from SCI.ELECTRONICS.DESIGN:

How do PROM bits get executed as instructions? --Wjbeaty 13:36, 23 November 2006 (UTC)

Takeoff
Why are we asked to open (or is it close?) the blinds and the lights inside the airplane switched off while taking off? (I am not sure if this practice is still followed) -- WikiCheng | Talk 11:54, 22 November 2006 (UTC)
 * It is a safety measure. The blinds have to be open in order for the cabin crew to be able to detect possible dangers outside the aircraft more easily. The lights are dimmed down so that our eyes would adapt to the dim light and not be suprised by darkness in case of an emergency. (Takeoff and landing are the most dangerous parts of a flight.) See this page for more about airline safety. –m y s i d ☎ 12:49, 22 November 2006 (UTC)

Thanks a lot!. -- WikiCheng | Talk 05:09, 23 November 2006 (UTC)


 * Expanding on that answer, looking out the windows would be hindered if the lights inside were too bright. Especially when it's dark outside, because they would become mirrors. DirkvdM 08:12, 23 November 2006 (UTC)


 * I found a New Scientist Last Word column that may be of interest. I think it's here but I don't have access to the archives so maybe I'm wrong. Fortunately, I also found it is available on the internet archive  Nil Einne 07:12, 25 November 2006 (UTC)

Body and protiens
Asked on the misc ref desk, but was told to ask here. What is the difference between high biological value protiens and low biological value protiens? I can't make any sense of our article on Biological Value, so I have no idea. Also, why exactly do the dietary requirements of male and femals differ? Is it something to do with body weight? And how it is normally seen that men are more active than women? Cheers. 81.131.65.176 16:59, 22 November 2006 (UTC)


 * The dietary reqs vary because of physical diffs. For example, women lose iron during menstruation, so need more iron than men.  They also lose calcium during breast-feeding, so need more calcium.  And, if pregnant, they need a lot of everything, so they can "build" a baby from scratch. StuRat 18:59, 22 November 2006 (UTC)


 * Now we know why women are so demanding. It's biological. :) DirkvdM 08:14, 23 November 2006 (UTC)


 * Proteins are formed as compounds of simpler molecules called amino acids (there's about 23 different amino acids if I remember correctly). Now our bodies don't need all these amino acids in the same amounts. Some proteins have lots of the 'more useful' amino acids, some have more of the 'less useful' amino acids. To a large degree the biological value of a protein will be determined by this mix of amino acids.
 * Re men being more active than women. I'm not even sure this is true. To the extent that it is, it could be partly cultural reasons, partly hormonal (e.g., testerone leading to increased competitiveness), partly to do with other biological factors such as the loss of iron mentioned causing a loss of energy, and I'm sure many other possible reasons. --jjron 10:19, 23 November 2006 (UTC)

Fat/institutionalized budgerigar question.
I was recently given a budgerigar. The bird was a pet, bought for the previous owner's kids, who eventually got sick of him, so he ended up with me. The bird is about three, is very overweight and I don't think he's ever even been out of his cage. He is tame though. Does anyone have any suggestions as to how I can get him to enjoy coming out and flying, so he can burn off some of that fat (I've already given him a better diet)? At the moment, when I open the cage door, he recoils in terror, as though the outside world and freedom is the worst thing in the world. He'll sit on my hand but he won't let me take him out of his 'cell'. I tried picking him up and putting him on top of his cage but when he saw all the open space, he just sat there and cowered until I put him back in. Any ideas would be appreciated. --84.67.52.115 17:04, 22 November 2006 (UTC)


 * My suggestion would be to leave the cage door open and let him come out in his own time, expect droppings though...87.102.36.82 17:48, 22 November 2006 (UTC)


 * I agree, all that's needed is time. I had a new cat that was terrified of everything and hid behind the furnace for 3 days.  He eventually got over his fear and came out.  To speed things along, though, you might want to leave a treat just outside the open cage door.  Then, once he takes that, leave another treat a bit farther away, until he is crossing the room for his treat. StuRat 18:55, 22 November 2006 (UTC)


 * A bird may panic and fly away from you at first. You might start with a small room(like a bathroom) where it will be simple to catch the bird, rather than chasing him all over the house so he gets too over heated or has a heart attack from the unaccustomed exercise of flying around. He may fly into windows or mirrors and become injured, so it is best if they are covered. Fans must be turned off. A sink with water in it is very dangerous; the bird may drown in a short while. If there is an open door or window, of course the bird is likely to get out and be lost. Birds instinctively go "up" If you remove the food and water, take the bottom off the cage, and slowly turn it upside down, the bird will come out the open bottom (now the top). A bird afraid to come to you will enter the cage through the open bottom (with it right side up. Stick to a few minutes of flying the first few sessions. It will likely hop up on your finger more willingly outside the cage than in it. Edison 18:57, 22 November 2006 (UTC)


 * I don't think the bird will go for that. If you start forcing him to do things he doesn't want to, he'll grow to resent you and just kick up more of a fuss and start getting vicious with you. Birds (parrots at least) work on incentives and trust. Forcing the bird out of his cage is the equivalent of keeping a human in solitary confinement for several years, then blindfolding him, loading him into the back of a truck and dumping him in a layby. --Kurt Shaped Box 23:58, 22 November 2006 (UTC)

 I have a little budgie/He is my very pal/I take him walks in Britain/I hope I always shall/I call my budgie Jeffrey/My Granddad's name's the same/I call him after Granddad/Who had a feathered brain. Beginning of "The Fat Budgie" by John Lennon. --jpgordon&#8711;&#8710;&#8711;&#8710; 20:23, 22 November 2006 (UTC)

RPET
Hello,

I work in global marketing for an audio electronics company. We're in a transitional phase with our consumer packaging, which is now composed primarily of PVC. I found information on PET as a possible alternative, but nothing about RPET, which I believe contains a certain percentage of recycled PET. Does anyone know more about PVC vs. PET and PET vs. RPET in terms of environmental impact?

Thanks for your help, stook &#124; &#91;&#91;User talk:stook&#124;]] 17:31, 22 November 2006 (UTC)
 * rpet appears to stand for recycled or reprocessed PET see http://www.extechplastics.com/en/PET/rpet.php.
 * There have been numerous issues raised with the safety and enviromental safety of PVC.
 * For PET see Polyethylene terephthalate
 * Usually you would ask your packing supplier questions like these. They should be able to give you all the sales talk on the advantages of each type of material. If your interested in biodegradable packaging why not consider cardoard.87.102.36.82 17:45, 22 November 2006 (UTC)


 * ...for PVC, check out our article Polyvinyl chloride. --HappyCamper 18:47, 22 November 2006 (UTC)
 * Both PVC and PET have aroused the hate of tree huggers at some time or another - PVC for possible heavy metal contamination and production of dioxins when burnt. I think PET has been linked to hormone altering compounds - see phthalate.
 * Possibly there are alternatives - polystyrene, Polpropylene. or take a look at Category:Biodegradable plastics for plastics with green credentials.

Discharging a Capacitor
What is the best way to discharge a very big capacitor safely with no specialist equipment? Many thanks, --86.139.127.29 20:49, 22 November 2006 (UTC)


 * Depends somewhat on the voltage to which the capacitor is charged. However, the standard safe practice is to connect a reasonably high value resistor across it. The resistor value should be great enough to limit the peak discharge current to reasonable values for the size of capacitor. For very high voltages (20kV) I used to use a 5 Mohm resistor. But for a couple of hundred volts or so, I think a 10 k resistor would do. --Light current 21:04, 22 November 2006 (UTC)


 * Very carefully.... Yep, Light current's suggestion should work quite well.  Note that the current through the resistor (when the discharge starts) is going to be equal to the capacitor's potential in volts divided by the resistor's value in ohms; make sure that you're not going to melt the resistor with a high current.  Also be careful – if you're working at very high voltages – that electricity won't be able to arc around the resistor, or from the leads into your body. TenOfAllTrades(talk) 00:14, 23 November 2006 (UTC)


 * Yeah the resistors we used at 20 kV were about 6" long attached to the end of an earthing stick!--Light current 00:45, 23 November 2006 (UTC)


 * Yep, small quarter-watt resistors are only good for 500V or perhaps 1000V.  To make a high-volt resistor, just solder lots of small resistors in series, where 10KV would use 20 resistors.   Also note:  some large capacitors cannot tolerate direct discharge.  Any small imperfections in their foil electrodes will lead to cracks in the foil which grow perpendicular to the current path.  (This same effect is seen when a CDROM is cooked in a microwave oven.)   Your big capacitor might work fine after a direct discharge, but each later discharge might add to a growing crack, until suddenly the connections between the terminals and the foil have broken entirely.  On larger Tesla coils with home-built capacitors you can sometimes see this process in action, as tiny cracks start in the edge of the narrow foil connections and slowly eat their way across. --Wjbeaty 13:18, 23 November 2006 (UTC)


 * However, Im not sure if large HV caps have the max discharge (or charge) current printed on them, so you may have to look up the manf data sheet. BTW I think the 10" or 12" resistors we used were good up to about 50kV, but as WJB says, you could always connect two (or more) in series for higher voltage withstand. 8-|--Light current 17:53, 23 November 2006 (UTC)


 * Also it's worth noting that for high voltages (in the kV region), the diameter of the resistors (esp the end caps) must be great enough to avoid corona discharge and HV resistors are not usually soldered together but screwed into each other so that the overall diameter is maintained. The HV resistors I'm familiar with were about 1" dia.--Light current 18:00, 23 November 2006 (UTC)


 * Personally, I recommend a screw driver. Works like a charm. Oh but remember to put a camera to record it first. The Darwin Awards is always looking for candidates (NB THIS IS A JOKE, DON'T EVEN THINK OF TRYING THIS) Nil Einne 16:03, 24 November 2006 (UTC)


 * THe OP was looking for the best way, not the most explosive! 8-(--Light current 16:14, 24 November 2006 (UTC)

Carbon dioxide
If only 0.04% of carbon dioxide enters the body by inhaling, How does an extra 4% come out. How is this extra carbon dioxide produced


 * It is produced through cellular respiration; specifically, through aerobic respiration. — Knowledge Seeker দ 23:45, 22 November 2006 (UTC)


 * The function of the lungs is for the body to exchange molecules with the air, more specifically take in oxygen and getting rid of carbon dioxide. If the concentrations in inhaled and exhaled air were the same, there would have been no exchange. DirkvdM 08:20, 23 November 2006 (UTC)


 * A product of combustion?--Light current 03:03, 24 November 2006 (UTC)